The study is published by researchers Brian S. Mautz et al.
in the April, 2013 edition of the medical journal Proceedings of the National Academy of Sciences
, and is titled: "Penis size interacts with body shape and height to influence male attractiveness."
It found that human females definitely rate men with larger penis and body size more attractive than smaller men.
The researchers concluded that prehistoric women with visual access to the genitals of their scantily clad men exercised their preference for bigger penises to influence the evolution of the unusually large genitalia of human males compared to other primate species such as chimpanzees and gorillas.
The researchers approached the study with the assumption that previous studies may have unwittingly introduced a bias when they asked women about their preference too directly. Medical Express
reports that according to the lead author Brian Mautz, a postdoctoral researcher in evolution and sexual selection at the University of Ottawa: "Since penis size is a sensitive subject, it's hard to determine whether females lied or 'self-deceived' in their responses."
To address the bias that may have arisen in study designs that directly asked women about their size preference, the team used computer-generate images of generic male figures with various heights, body conformations and flaccid penis size.
created 343 male figures with different combinations of height, shoulder-to-hip ratio and penis size, all within a normal range. They then asked a sample of 105 heterosexual Australian female volunteers to view a random sampling of 53 of the CGI figures and to rate their attractiveness. The figures could be rotated and viewed at different angles.
The women were not told that they were participating in a study about penis size.
On analysing the data, the researchers
found that the woman rated tall men with long penises as the most attractive and tended to gaze longer at them. The found that flaccid penis size, height and shoulder-to-hip ratio were all important elements of a woman's assessment of the attractiveness of the male figures
But the traits interacted in a complex pattern: Penis size had greater impact on male attractiveness in taller men than in shorter men. That is, while a big penis made a shorter male figure more attractive, it had a bigger effect on the female assessment of the attractiveness of a taller male figure.
Women placed so much emphasis on penis size that the study authors were forced to conclude that female preference for men with big penises must have driven the evolution of bigger penises among humans compared to primates. The researchers
suggested that prehistoric men who dressed scantily had less opportunities to hide the size of their penis from the women compared to modern men who wear clothes which conceal the vital information that women seek.
According to the abstract
Before clothing, the nonretractable human penis would have been conspicuous to potential mates. This observation has generated suggestions that human penis size partly evolved because of female choice. Here we show, based upon female assessment of digitally projected life-size, computer-generated images, that penis size interacts with body shape and height to determine male sexual attractiveness. Positive linear selection was detected for penis size, but the marginal increase in attractiveness eventually declined with greater penis size (i.e., quadratic selection).
Penis size had a stronger effect on attractiveness in taller men than in shorter men. There was a similar increase in the positive effect of penis size on attractiveness with a more masculine body shape (i.e., greater shoulder-to-hip ratio). Surprisingly, larger penis size and greater height had almost equivalent positive effects on male attractiveness. Our results support the hypothesis that female mate choice could have driven the evolution of larger penises in humans. More broadly, our results show that precopulatory sexual selection can play a role in the evolution of genital traits.
The researchers found that attractiveness rating increased with size but at a diminishing rate after a point. According to Mautz
: "We didn't find an ideal (i.e. 'most attractive') penis size or height. The attractiveness scores were still increasing at the largest values for these traits" (although at a diminishing rate).
Women's ages did not affect the manner in which they rated the male figures but their height did. Taller women placed more emphasis on height than shorter women. Women were also found to take more time to rate the figures they found more attractive. The finding agrees with the result of previous studies that found that people tend to gaze longer at objects they found more attractive.
The researchers concluded that the results "directly contradict claims that penis size is unimportant to most females." It also provides answers to the question why human males have much larger genitalia when compared to other primates.
However, the disproportionate impact of female sexual selection on the size of human male genitalia compared to body size may suggest that the preference of women for bigger, taller men may have evolved in the social context independent of preference for genital size. Prehistoric women would tend to choose bigger men only because in the circumstances of primitive life, a bigger, brawnier man affords more protection than a smaller one.
Seventy percent of the women used in the study were of European origin, 20 percent Asian and seven percent other ethnic backgrounds.
The average age of the females was 26.